1. Field of the Invention
Embodiments of the present invention relate to a photovoltaic cell, and in particular, to an apparatus for manufacturing a photovoltaic cell including a chalcogen material and a method for manufacturing a photovoltaic cell including a chalcogen material.
2. Description of the Related Art
Development of alternative energy resources, in particular, solar energy resources, is actively carried out to stave off depletion of petroleum resources. The development of solar energy resources is mainly performed by solar light power generation obtained by converting solar energy into electric energy, and is focused on the development of highly efficient photovoltaic cells.
Photovoltaic cells have a p-n junction in which a p-type semiconductor layer contacts an n-type semiconductor layer. Solar light reaches the p-n contact to generate photoelectromotive force, and thus, electric energy is generated. Currently, silicon semiconductor-based photovoltaic cells, which are a first generation photovoltaic cell, are typically used. However, due to requirements regarding lightweight and thin structures, manufacturing costs, productivity, and production applicability, compound thin film photovoltaic cells, which are second generation photovoltaic cells, are being developed as an alternative.
A chalcopyrite-based compound semiconductor material, such as CuInSe2, may be used as a material for use as a light absorption layer in a compound thin film photovoltaic cell. Such a chalcopyrite-based compound semiconductor material has a direct transition-type energy band gap and the highest photoabsorption coefficient of 1×105 cm−1 from among semiconductors. A chalcopyrite-based compound semiconductor may enable manufacturing of high-efficient photovoltaic cells in the form of a thin film having a thickness of 1 μm to 2 μm, and may retain high electroptical stability for a long period of time.
CuInSe2 has a band gap of 1.04 eV. Accordingly, to adjust the band gap to be an ideal band gap of 1.4 eV, a portion of indium (In) may be substituted with gallium (Ga), and a portion of selenium (Se) may be substituted with sulfur(S). For reference, CuGaSe2 has a band gap of 1.6 eV, and CuGaS2 has a band gap of 2.5 eV. A four-membered compound including copper-indium-gallium-selenium is referred to as CIGS, and a material including copper-indium-gallium-selenium-sulfur is referred to as CIGSS.
However, since CIGS and CIGSS are poly-membered compounds, it is difficult to form a light absorption layer by using such materials. In addition, since a selenization reaction used in the manufacturing process for a light absorption layer requires toxic and corrosive H2Se gas, the selenization needs to be performed with a great deal of caution. Manufacturing costs may be high due to the need for installation of a special waste processing apparatus. In addition, selenium is highly likely to form a high molecular weight gas when it forms a selenium layer by deposition or evaporation, and when selenium is exposed to a small temperature gradient in a chamber, it may quickly solidify with a heterogeneous structure. Thus, the formed light absorption layer may have a heterogeneous selenium concentration gradient, thereby leading to a decrease in chalcogenation and an increase in surface roughness. Such problems may result in a decrease in efficiency of a photovoltaic cell.